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We use recent data that show a narrow peak around $\sqrt{s}=2.37\ \text{GeV}$in the $pn \to d \pi^+ \pi^-$ cross section, with about double strength at thepeak than in the analogous $pn \to d \pi^0 \pi^0$ reaction, and, assuming thatit is due to the excitation of a dibaryon resonance, we evaluate the crosssection for the $pn \to pn \pi^+ \pi^-$ reaction, with the final $pn$ unboundbut with the same quantum numbers as the deuteron. We use accurate techniquesto determine the final state interaction in the case of the $pn$ forming adeuteron or a positive energy state, which allow us to get the $pn \to pn \pi^+\pi^-$ cross section with $pn$ in I=0 and S=1, that turns out to be quite closeor saturates the experimental $pn \to pn \pi^+ \pi^-$ total cross sectionaround $\sqrt{s} = 2.37\ \text{GeV}$, depending on the angular momentumassumed. We then parametrize a background with different methods, and the sumof the resonant and background contributions is fitted to present data. Theresulting cross section exceeds the experimental results in the region of theresonant peak, showing a problem in the dibaryon hypothesis. Yet, in view ofthe dispersion of present experimental data, and the scarce information around$\sqrt{s} = 2.37\ \text{GeV}$, a call is made for precise measurements of the$pn \to pn\pi^+\pi^-$ reaction around this energy, to further clarify thisissue.

Constraints on a possible dibaryon from combined analysis of the $pn \to d \pi^+ \pi^-$ and $pn \to pn \pi^+ \pi^-$ cross sections